Technical Abstract:
The project is investigating the possibility of using the mineral (ionomics) composition of rice (Oryza sativa L.) seedling leaves to predict varieties that accumulate large amounts of certain minerals in their seeds. This information will be used for improving our understanding of the mineral physiology of rice and other plants, and for genetically improving the nutritional value of rice grain. In 2007 and 2008, preliminary field trials were conducted on 1600 varieties from the USDA world germplasm collection. These flooded and unflooded trials identified rice varieties with varying levels of seed mineral composition. The objective of the presented study was to establish correlations across varieties between seedling-leaf and seed mineral contents such that leaf data could be used to predict seed content for certain minerals, with an initial emphasis on K, Fe, Zn, and Mo. This would greatly accelerate the selection process for desirable seed mineral traits. The 40 varieties selected for their extreme seed mineral composition were grown in an outdoor potted plant study in 2010. All 40 varieties were planted in 7-to-10 day intervals to provide on a single sampling date, plants of a wide range of developmental stages. Leaf tips (5 cm) for ionomic analysis were collected from the most recently fully emerged leaf. Rice varieties from Malaysia (GSOR accessions 310354, 310355, 310356, 311643, and 311743) with high seed Mo also displayed high leaf Mo, indicating that leaf data can be used to predict seed Mo. However, rice varieties with high seed K, Fe, and Zn did not show any such correlation. The high seed and leaf Mo in these Malaysian varieties is hypothesized to be due to a root-localized trait and to be related to an acid-tolerance mechanism, as these Malaysian soils are highly acidic (pH 4.7). Future study will quantify growth and physiology of roots and shoots of varieties varying in Mo content when grown under different pH regimes.